This invention relates to an improved liquid oxygen (LOX) compatible biodegradable dye penetrant composition and method for non-destructively testing material specimens to locate and identify surface voids, cracks or defects, prior to contacting such parts with liquid oxygen. The invention is especially concerned with a novel generally easily water washable, stable and sensitive dye penetrant composition of the above type having the characteristics of being able to disclose a wide range of defective conditions in parts, employing as solvent or vehicle essentially a biodegradable nonionic surfactant in the form of certain oxyalkylated alcohols, preferably ethoxylated alcohols, and mixtures thereof, and incorporating an additive to render the composition compatible with liquid oxygen (LOX); and to a method utilizing such dye penetrant composition for nondestructive testing of parts subsequently contacted with liquid oxygen.
Dye penetrants are highly useful materials for nondestructive testing of metal work piece surfaces. In many important and expensive mechanical devices, it is necessary to inspect every metal component of the system for structural defects, prior to final fabrication. Dye penetrants are particularly useful in decreasing inspection processing time and can be highly sensitive in detecting microdefects in metal components of aluminum, steel, nickel, titanium and the like.
In known penetrant inspection methods for rapid location and evaluation of surface flaws or cracks in test bodies or parts, a dye penetrant composition, preferably containing a fluorescent dye, and which will penetrate the openings of the surface cracks or flaws in the part, is applied to the surface of the test body, and the excess penetrant composition is removed from the surface of the body. A developer composition may then be applied to the part surface, which acts as a wick and causes the liquid penetrant containing the fluorescent dye, which was retained in the cracks or surface flaws, to be drawn up out of the surface defects by capillary action. The part is then exposed to appropriate lighting conditions, such as invisible fluorescigenous light, and the location of the surface flaws is revealed by the emission of visible fluorescent light by the penetrant dye which was retained in the cracks or flaws after the penetrant composition was removed from the surface of the part.
For best efficiency, particularly for the detection and location of minute surface cracks and flaws, as well as intermediate size and gross cracks, it is necessary that the dye penetrant have high sensitivity.
In addition, stability of the penetrant solution is essential without the necessity for carefully balancing the various liquid components of a dye penetrant solution in order to obtain efficient penetration of the solution into the cracks and flaws of a part, dye solubility, wetting action and washability control.
An additional criterion has recently developed also with respect to dye penetrant solutions and compositions. Generally, dye penetrant solutions presently being used and containing solvents and wetting agents present a disposal problem in that they are substantially non-biodegradable, that is, they are very difficult to decompose by bacteria in sewage disposal plants. Hence the necessity for the development of dye penetrant solutions and compositions which are biodegradable, that is which employ dye solvents and carriers which are biodegradable, and are readily available despite the petrochemical shortage, has attained considerable importance.
In my U.S. Pat. Nos. 3,915,885 and 3,915,886, there are disclosed novel dye penetrants which have improved washability and sensitivity characteristics, and which are biodegradable, containing as the vehicle for the dye, certain biodegradable nonionic oxyalkylated alcohols.
Further, where the parts to be inspected are to be later subjected to contact with LOX or a like strong oxidizer, it is particularly desirable that the inspection system, and the dye penetrants used in inspection do not increase the danger or sensitivity of the mechanical components to reaction with such strong oxidizers including LOX. For example, a large rocket propellant motor may use LOX, or a like strong oxidizer, in the rocket propellant. It is quite important under these circumstances that the LOX not be reactive with any traces or residues of the inspection dye penetrant which may remain in the cracks or defects of the inspected propellant tanks or other components, fabricated from inspected metal stock after cleaning.
In my U.S. Pat. No. 3,753,647 there is disclosed a liquid dye penetrant which is compatible with liquid oxygen and which comprises N-methyl-2-pyrrolidone, a mixture of a ketone and wetting agents, a fluorescent dye and a halocarbon. Although such dye penetrant composition has been found effective, it has the disadvantages of requiring a multiplicity of dye carriers or solvents, with proper balance thereof necessary to provide a desired sensitivity, and the composition is not biodegradable.
In my copending application Ser. No. 577,958, filed May 15, 1975, now U.S. Pat. No. 3,989,949, there is disclosed an improved liquid oxygen compatible dye penetrant which is biodegradable, employing as solvent or carrier for the dye certain biodegradable nonionic surfactants comprised of ethoxylated liner alcohols as described in my U.S. Pat. No. 3,915,886, and a halocarbon.
However, both of the above described dye penetrants containing a halocarbon, particularly a chlorinated hydrocarbon, and which are nonflammable type solvents, are incompatible for use with certain metals, particularly with steel surfaces, which are sensitive to attack by chlorinated hydrocarbons.
Accordingly, an object of the present invention is the provision of a readily water washable biodegradable liquid oxygen compatible dye penetrant solution or composition which is of simple formulation and which does not require the use of mixtures of conventional solvents and wetting agents, and which is formed of an essentially single or sole nonionic surfactant, and which is highly stable, has excellent sensitivity and is essentially non-toxic. A particular object of the invention is to provide a dye penetrant solution of the above noted type, and which incorporates a nonhalogenated additive which eliminates the hazard of traces of dye penetrant reacting explosively with liquid oxygen or other strong oxidizers, substantially, without affecting the biodegradability or sensitivity of the dye penetrant, such additive being of a type rendering such dye penetrant compatible with a wide range of metal surfaces including steel alloys. A still further object is the provision of procedure employing such novel biodegradable and LOX safe dye penetrant composition for inspection of cracks, flaws and metallurgical conditions in metal structural components which are later to be placed in contact with liquid oxygen.